Registering shared wasm memory with the memory tracker was implemented to
track which instances need to be upated across threads on grow. As the
growing of memory when it is shared is behind a flag, the registering
should also be gated by the flag so as to not create global handles
that keep the memory alive.

Bug: v8:9075
Change-Id: I379a19413befa281cd384c9167fbc22ba52f4c2c
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1646882Reviewed-by: Bill Budge <bbudge@chromium.org>
Commit-Queue: Deepti Gandluri <gdeepti@chromium.org>
Cr-Commit-Position: refs/heads/master@{#62043}